The open-door helicopter tour in which five people died in a crash landing in the East River off Manhattan on Sunday was operating under safety restrictions reserved for photography flights that are looser than those for commercial air-tour rides.

Federal regulations exempt certain operations, including crop-dusting and aerial firefighting, from some of the safety rules that apply to commercial operators. It includes “aerial photography or survey” operations in that category.

The ill-fated New York flight was operating under that standard, according to a person familiar with the operation, who asked not to be named because the National Transportation Safety Board is still investigating. Commercial air tours are governed by separate regulations.

The passengers, who booked a photo tour of New York City at sunset, were wearing harnesses that tethered them to the aircraft and were equipped with knives designed to cut themselves free in the event of an emergency, photographer Eric Adams, who was on another helicopter operated by the same company at the same time, wrote in an account for an online publication called The Drive.

The harnesses were required because the helicopter’s doors had been removed so that participants could more freely photograph New York. Such a flight would not have been permitted under the regulations that govern air-tour flights, said the person.

“We are giving urgent attention to the use of harnesses specifically for aerial photography flights,” the Federal Aviation Administration, which oversees the aerial industry, said in an emailed statement. “We are supporting the NTSB and we will take appropriate action based on what we learn from the investigation.”

“As a matter of overall safety awareness, we are preparing further communications and educational outreach to aerial photography operators and consumers on the use of these harnesses,” the agency said.

The helicopter went down in the East River about 7 p.m. after the pilot radioed that he’d lost power. Within seconds, the Airbus SE AS350B2 helicopter turned over and sank. The pilot was able to escape and was rescued, but the five passengers had to be cut loose from the craft by divers, New York Fire Department Commissioner Daniel Nigro said.

The NTSB hasn’t yet released detailed information on what regulations governed the photo flight. Investigators have recovered a GoPro camera from the wreckage and will attempt to analyze any video it captured of the accident, the NTSB said in a statement Tuesday.

"I’m shocked by the tethering and the lack of a quick release," said Shawn Coyle, a helicopter pilot, safety consultant and author of books on flying. “The fact that five of them couldn’t get out means that it was pretty desperately bad. It’s not like seat belts on an airplane where you just undo the buckle and away you go.”

$99 for 10 Minutes

Tickets for the doors-off photography flight were sold by FlyNYON, which advertises on its website such services in cities including New York, Las Vegas and San Francisco. Prices range from $99 for 10 minutes to $2,000 to photograph New York’s New Year’s celebration, according to the website.

“FlyNYON takes the thrill of shooting images from an open-door helicopter and makes it accessible to everyone,” the company says on its website.

The helicopter was operated by Liberty Helicopters, which conducts air tours in New York.

The companies didn’t respond to telephone and emailed requests for comment but a statement on Liberty’s website said it was "fully cooperating with the FAA and NTSB investigations."

The growing number of air-tour companies operating similar doors-off flights has been alarming to some in the helicopter industry, said one person familiar with internal debates on the subject.

Allowing passengers to dangle their feet out of helicopters hundreds of feet in the air and using the harnesses designed for professional aviators runs counter to the safety goals of more traditional operators, said the person, who asked not to be named while the NTSB is investigating.

The accident has prompted several lawmakers to call for a temporary halt of helicopter tourist flights around New York.

“At minimum, these flights should be suspended until there can be an exhaustive review of the safety hazards of operating these flights in such a congested urban airspace,” said a release Tuesday from Representatives Jerrold Nadler, Nydia Velazquez and Carolyn Maloney, all New York Democrats.

The Senate’s top Democrat, Chuck Schumer of New York, issued a similar call aimed at Liberty on Monday.